Various known designs of wind turbine structures include the common propeller blade type turbine, the so-called Darrieus blade type turbine, and the so-called Savonius blade type turbine.
Several Savonius or “S”-rotor blade designs are known, including those typified in Canadian Patent No. 1,236,030, EPO Publication No. 0040193 B1, French No. 961,999, German No. 187865, Japanese Publication No. 60-090992, Swedish No. 65,940, WIPO No. WO/99/04164, and U.S. Pat. Nos. 1,697,574 and 4,293,274. Each of those various Savonius-type blade designs have inherent limitations, including the limitation of noise during operation, excessive vibration during operation, a tendency to “run away” during elevated wind speed operations and often excessive drag created during rotation of the leeward or non-wind-gathering portion of the blade's movement.
Further, various Darrieus-type turbine blade designs are disclosed in U.S. Pat. Nos. 1,835,018, 2,020,900, 4,112,311, 4,204,805 and 4,334,823. However, these Darrieus-type designs also have inherent deficiencies, including that only the middle one-third of their blade length (at least for curved Darrieus blade versions) efficiently creates power; that the farther the distance from a curved blade to its axis of rotation, the greater the likelihood, especially in large scale power generation units, of a Darrieus type unit going into harmonic vibration and self-destructing; that all such Darrieus-blade type units are not self-starting, but need assistance in starting; and that in many wind conditions they can, on a periodic basis, use up more energy than they actually produce. Without proper controls and/or mechanical braking systems, Darrieus type units (like Savonius units) have been known to “run away” during elevated wind speed conditions.
Further yet, there have been attempts at combining a bucket-shaped Savonius-type drag blade system with a Darrieus-type curved lift blade system, as found in U.S. Pat. No. 3,918,839, and in Tanzawa, et al., “Dynamic Characteristics of the self-controlled Darrieus-Savonius Hybrid Wind Turbine System,” Proceedings of the CSPE-JSME-ASME International Conference on Power Engineering, Vol. 1, (1995), pp. 115–121 (“Tanzawa”). Yet in U.S. Pat. No. 3,918,839, significant difficulties arose relative to the operational, i.e., rotational, stability of the unit at high wind speeds. In Tanzawa, the addition of a Savonius bucket rotor to start the Darrieus rotor resulted in a reduction in the total turbine power and high braking torque at higher rotational rates. There were also the above-noted inherent problems present in all separate Darrieus and Savonius-type blade systems.
Most available wind turbine designs have problems of excessive noise and vibration, often self-destruct in high wind conditions, some require separate start-up, braking or stopping mechanisms, and many are not considered safe, readily insurable or building-code permitted, at least not for use in congested urban settings.
Thus, there has been an ongoing need for a wind turbine design that can be successfully incorporated into various building and tower structures, that produces minimal noise and vibration during operation, is capable of starting up and operating in each of low speed, steady, gusty, and high speed wind conditions, has a built-in self-regulation via an inherent structural geometry against over-speeding runaway conditions, is formed of blade designs that operate in essentially all wind conditions and produce moderate drag during full rotational operation, which is easy to manufacture and ship, and which can be housed in a safe operating package for use in crowded urban settings.